This invention relates to a valve assembly, in particular of a kind intended for use in drillpipe.
As is well known, drillpipe is extensively used in the oil and gas industries. Drillpipe consists of lengths (referred to as “stands”) of rigid metal pipes that are cylindrical, are hollow and are capable of being threadedly secured one to another.
Drillpipe is introduced into a wellbore or other borehole typically in a “stand by stand” fashion in which successive stands are added from a surface location to drillpipe stands that are secured seriatim to one another and are already at least partly inserted into the wellbore. Each stand of drillpipe added in this way is lowered into the borehole in order to advance the assembled drillpipe along the wellbore until it reaches a chosen depth (that may be thousands or even tens of thousands of feet from the surface location).
Drillpipe is used in a wide variety of situations. It is usually inserted into a wellbore that has not been “completed”, i.e. the well has not been “cased”. This is achieved by running a liner and through the creation of a cement annulus that contains fluids in the geological formation surrounding the wellbore so as to prevent them from rising up the wellbore under naturally occurring pressure.
Drillpipe therefore must be capable of resisting the fluid pressures that arise in subterranean formations. To this end each stand of drillpipe is manufactured as a cylinder of a rigid metal (e.g. steel) that may easily accommodate such pressures when they act on the exterior surface of the drillpipe.
Each stand however is open at each end such that the drillpipe would, in the absence of precautionary measures, constitute a continuous pipe extending from one end, deep inside a wellbore, to the other at a surface location.
This feature of drillpipe is needed because in normal use the drillpipe is filled with a fluid that is pressurised to permit the conveying of objects (typically oilfield tools) along the drillpipe so as to protrude from the remote end of the drillpipe and perform an operation. From time to time however it may happen that fluid under pressure in the geological formation acts on the subterranean end of the drillpipe. If the pressure in such fluid is great enough it forces the drillpipe fluid (and, potentially, any objects in it) along the drillpipe towards and out of its surface end. This phenomenon is known as “kicking” of the well.
Aside from the fact that the emergence (possibly at great speed) of drillpipe fluid and objects from the drillpipe is potentially extremely hazardous, the action of formation fluid pressure inside the drillpipe may damage the drillpipe itself or any objects supported in it. In such a case it potentially becomes necessary to withdraw perhaps many tens or hundreds of stands of drillpipe from the wellbore and disconnect them one by one until the damaged section is at a surface location and can be replaced.
In some situations a damaged object inside drillpipe may become stuck. This makes it difficult to recover the object. This is inconvenient if the object in question is an expensive oilfield tool; and it may be very costly in terms of delays in “productionising” an oil or gas well.
In order to prevent formation fluid pressure from propagating along the whole length of a drillpipe certain stands that are installed at intervals along drillpipe include flapper valves that close off the interior of the drillpipe to the passage of fluid.
As indicated the interior cross section of the drillpipe is circular and the known flapper valves typically consist of a circular valve member that is of the same diameter as the drillpipe interior.
Such a valve member is pivotably secured at one edge to the inside of the drillpipe wall. A spring acts between the valve member and the drillpipe wall to force the valve member towards a closed position. The drillpipe includes an annular shoulder or similar formation against which such spring pressure forces the outer edge of the valve member so as to seal the drillpipe.
The spring acts in one direction only on the valve member. The valve is configured such that any formation fluid pressure (or other fluid pressure) acting inside the drillpipe acts in the same direction thereby sealing the drillpipe more firmly. Thus in the event of the well kicking the formation fluid pressure tends to enhance the sealing provided by the flapper valve and prevent the formation fluid from having the deleterious effects mentioned above.
Drillpipe is used to convey well survey tools to great depths in wellbores. On such occasions the tools are lowered through the drillpipe (usually but not always supported on wireline, the nature and functions of which will be familiar to those of skill in the art) to protrude at the downhole end. They may perform surveying and logging operations before being retrieved to a surface location.
A tool deployed in this fashion typically engages a landing ring formed in the drillpipe stand at the downhole end of the drillpipe. The landing ring prevents the tool from emerging completely from the drillpipe, with the result that the tool protrudes while being retained captive relative to the drillpipe. The exposed tool then logs data from the formation and stores it in an on-board memory for later use.
In an example such as this there may be no direct communication link between the tool and the surface location (where operators such as logging engineers and analysts may be located together with computers that are capable of processing signals, generated by the tool, into data that may be stored and/or presented as logs). Therefore it is necessary to retrieve the tool to a surface location before it will yield any useful data.
Even when the tool remains connected by wireline to the surface location during logging it is essential to retrieve the tool to the surface after logging activity has ceased.
The flapper valve described above is suitable to permit deployment of the tool in the downhole direction. This is because as the tool approaches the valve member either the pressure of pumped drillpipe fluid, or physical engagement of the tool with the valve member, is enough to pivot the valve member to its open position against the action of the spring.
On the other hand the nature of the flapper valve prevents return of the tool in the uphole direction by reason of the normally closed, one-way nature of the valve member. Therefore until now the only technique available for retrieving a landed tool has been to withdraw the drillpipe stand by stand.
This is very time-consuming and is particularly undesirable if it is required to leave the drillpipe in position following a logging operation.
The invention seeks to solve or at least ameliorate one or more disadvantages of the prior art arrangements.
According to the invention in a first aspect there is provided a valve assembly comprising a pipe member defining a hollow, generally cylindrical interior having secured therein a valve member that is moveable between an open position, permitting passage of an object through the valve in first and second, opposite directions, and a closed position preventing passage of fluids along the pipe member in one of the first and second directions; and a resiliently contractile arm interconnecting the valve member and the pipe member so as to urge the valve member towards the closed position and such that when an object passes along the pipe member and engages the valve or the arm the valve member moves towards the open position.
Such an arrangement permits a deployed downhole tool, such as but not limited to a logging tool, to be pumped or withdrawn on wireline to an uphole location through the valve without having to remove the drillpipe via which it is deployed.
Conveniently the valve assembly includes a recess in which the valve member is receiveable when in its open position.
In a preferred embodiment of the invention the valve member includes a first pivot, on a first side, securing the valve member and the pipe member together; and a second pivot, on an opposite side, securing the valve member and the resiliently contractile arm together.
This arrangement ensures that drillpipe pressure acting in the downhole direction and/or contact of a conveyed tool with the valve member provides a sufficient force to open the valve member and permit the passage of an object such as a tool in the downhole direction.
Conveniently the first pivot lies at an edge of the recess. This arrangement is advantageously compact.
It is also preferable that the resiliently contractile arm is secured at a first end to the valve member and at a second end, that is remote from the first end, to the pipe member.
This feature ensures that even when a tool or other object is pulled in an uphole direction it encounters a part of the valve against which it may bear in order to achieve opening of the valve to permit its uninterrupted passage up the drillpipe.
In a preferred embodiment of the invention the resiliently contractile arm includes a first, hollow arm member having slidably received therein a further, hollow arm member, the first and further arm members being interconnected inside the first said member by a resiliently deformable element. Other arrangements of the contractile member however are possible within the scope of the invention.
In a second aspect the invention resides in a method of using a logging tool comprising the steps of:                (i) causing the tool to move in a downhole direction along drillpipe including at least one valve assembly as defined herein such that the tool passes through at least one said valve assembly in a forward direction;        (ii) deploying the tool at the downhole end of the drillpipe;        (iii) subsequently causing the tool to move in an uphole direction along the drillpipe such that the tool passes through at least one said valve assembly in a reverse direction.        
Conveniently the step (i) includes contact between a downhole part of the logging tool and the valve member so as to urge the valve member towards its open position; and the step (iii) includes contact between an uphole part of the logging tool and the resiliently contractile arm, also so as to urge the valve member towards its open position. Such contact between a downhole part of the logging tool and the valve member however may not always be needed. It may be possible to open the valve, when it is desired to move the logging tool in a downhole direction, using drillpipe fluid pressure alone.
It is further preferable that when moving along the drillpipe the logging tool is connected to wireline.
When the logging tool is so configured optionally the method includes the sub-step of, after step (ii), disconnecting the logging tool from wireline to which it is connected. Following such disconnection, or if the logging tool is initially deployed without the use of wireline, the method of the invention may include the optional sub-step of, before step (iii), connecting the logging tool to wireline.
It is however possible to perform the method of the invention without making use of wireline at all. To this end in an alternative embodiment the method of the invention may be such that when moving along the drillpipe the logging tool is pumped under the influence of drillpipe fluid pressure. This version of the method is of particular benefit when the logging tool is of the compact battery/memory (or “slimhole”) type, although it may also be practised when using other logging tool types.
Preferably therefore the tool includes an on-board memory, and the method includes the step of operating the tool following deployment at the downhole end of the drillpipe in order to record in the memory data pertaining to a geological formation in the vicinity of the said downhole end.
It is also preferable that the method includes the step of, after causing the tool to move in an uphole direction, retrieving the tool to a surface location and downloading data stored in the memory.
Such steps permit the method of the invention to be of particular utility in the data logging art.
As used herein the terms “uphole” and “downhole” are to be construed in accordance with their conventional meanings in the oil and gas drilling art, as will be known to the worker of skill. In consequence the valve assembly of the invention normally is installed such that the resiliently contractile arm lies on the downhole side of the valve member. It may however be desirable from time to time to install the valve assembly such that the contractile arm lies on the uphole side of the valve member.
Such use of the valve assembly is believed to be only rarely desired, but for the avoidance of doubt it nonetheless lies within the scope of the invention.